Sestrin2: A Promising Therapeutic Target for Liver Diseases

Identification and Validation of Ferroptosis-Related Genes in Sevoflurane-Induced Hippocampal Neurotoxicity

Background

Sevoflurane is one of the most popular inhalational anesthetics during perioperative period but presenting neurotoxicity among pediatric and aged populations. Recent experiments in vivo and in vitro have indicated that ferroptosis may contribute to the neurotoxicity of sevoflurane anesthesia. However, the exact mechanism is still unclear.

Methods

In current study, we explored the differential expressed genes (DEGs) in HT-22 mouse hippocampal neuronal cells after sevoflurane anesthesia using RNA-seq. Differential expressed ferroptosis-related genes (DEFRGs) were screened and analyzed by Gene Ontology (GO) and pathway enrichment analysis. Protein-to-protein interaction (PPI) network was constructed by the Search Tool for the Retrieval of Interacting Genes (STRING). Significant modules and the hub genes were identified by using Cytoscape. The Connectivity Map (cMAP) was used for screening drug candidates targeting the identified DEFRGs. Potential TF-gene network and drug-gene pairs were established towards the hub genes. In final, we validated these results in experiments.

Results

A total of 37 ferroptosis-related genes (18 upregulated and 19 downregulated) after sevoflurane exposure in hippocampal neuronal cells were finally identified. These differentially expressed genes were mainly involved into the biological processes of cellular response to oxidative stress. Pathway analysis indicated that these genes were involved in ferroptosis, mTOR signaling pathway, and longevity-regulating pathway. PPI network was constructed. 10 hub genes including Prkaa2, Chac1, Arntl, Tfrc, Slc7a11, Atf4, Mgst1, Lpin1, Atf3, and Sesn2 were found. Top 10 drug candidates, gene-drug networks, and TFs targeting these genes were finally identified. These results were validated in experiments.

Conclusion

Our results suggested that ferroptosis-related genes play roles in sevoflurane anesthesia-related hippocampal neuron injury and offered the hub genes and potential therapeutic agents for investigating and treatment of this neurotoxicity after sevoflurane exposure. Finally, therapeutic effect of these drug candidates and function of potential ferroptosis targets should be further investigated for treatment and clarifying mechanisms of sevoflurane anesthesia-induced neuron injury in future research.

Targeting on Nrf2/Sesn2 Signaling to Rescue Cardiac Dysfunction during High-Fat Diet-Induced Obesity

Obesity is of concern to the population because it is known to cause inflammation and oxidative stress throughout the body, leading to patient predisposition for health conditions such as diabetes, hypertension, and some cancers. However, some proteins that are activated in times of oxidative stress may provide cytoprotective properties. In this study, we aim to gain further understanding of the interconnection between Nrf2 and Sesn2 during obesity-related stress and how this relationship can play a role in cardio-protection. Cardiomyocyte-specific Sesn2 knockout (cSesn2^-/-) and Sesn2 overexpressed (tTa-tet-Sesn2) mice and their wildtype littermates (Sesn2^flox/flox and tet-Sesn2, respectively) were assigned to either a normal chow (NC) or a high-fat (HF) diet to induce obesity. After 16 weeks of dietary intervention, heart function was evaluated via echocardiography and cardiac tissue was collected for analysis. Immunoblotting, histology, and ROS staining were completed. Human heart samples were obtained via the LifeLink Foundation and were also subjected to analysis. Overall, these results indicated that the overexpression of Sesn2 appears to have cardio-protective effects on the obese heart through the reduction of ROS and fibrosis present in the tissues and in cardiac function. These results were consistent for both mouse and human heart samples. In human samples, there was an increase in Sesn2 and Nrf2 expression in the obese patients' LV tissue. However, there was no observable pattern of Sesn2/Nrf2 expression in mouse LV tissue samples. Further investigation into the link between the Sesn2/Nrf2 pathway and obesity-related oxidative stress is needed.

The functions and roles of sestrins in regulating human diseases

Sestrins (Sesns), highly conserved stress-inducible metabolic proteins, are known to protect organisms against various noxious stimuli including DNA damage, oxidative stress, starvation, endoplasmic reticulum (ER) stress, and hypoxia. Sesns regulate metabolism mainly through activation of the key energy sensor AMP-dependent protein kinase (AMPK) and inhibition of mammalian target of rapamycin complex 1 (mTORC1). Sesns also play pivotal roles in autophagy activation and apoptosis inhibition in normal cells, while conversely promoting apoptosis in cancer cells. The functions of Sesns in diseases such as metabolic disorders, neurodegenerative diseases, cardiovascular diseases, and cancer have been broadly investigated in the past decades. However, there is a limited number of reviews that have summarized the functions of Sesns in the pathophysiological processes of human diseases, especially musculoskeletal system diseases. One aim of this review is to discuss the biological functions of Sesns in the pathophysiological process and phenotype of diseases. More significantly, we include some new evidence about the musculoskeletal system. Another purpose is to explore whether Sesns could be potential biomarkers or targets in the future diagnostic and therapeutic process.

Knockout of AMPKα2 Blocked the Protection of Sestrin2 Overexpression Against Cardiac Hypertrophy Induced by Pressure Overload

Objectives: Sestrin2 (Sesn2) has been demonstrated to be a cysteine sulfinyl reductase and protects cells from multiple stress insults, including hypoxia, endoplasmic reticulum stress, and oxidative stress. However, the roles and mechanisms of Sesn2 in pressure overload-induced mouse cardiac hypertrophy have not been clearly clarified. This study intended to investigate whether sestrin2 (Sesn2) overexpression could prevent pressure overload-induced cardiac hypertrophy via an AMPKα2 dependent pathway through conditional knockout of AMPKα2.

Methods and results: Sesn2 expression was significantly increased in mice hearts at 2 and 4 weeks after aortic banding (AB) surgery, but decreased to 60–70% of the baseline at 8 weeks. Sesn2 overexpression (at 3, 6, and 9 folds) showed little cardiac genetic toxicity in transgenic mice. Cardiac dysfunctions induced by pressure overload were attenuated by cardiomyocyte-specific Sesn2 overexpression when measured by echocardiography and hemodynamic analysis. Results of HE and PSR staining showed that Sesn2 overexpression significantly alleviated cardiac hypertrophy and fibrosis in mice hearts induced by pressure overload. Meanwhile, adenovirus-mediated-Sesn2 overexpression markedly suppressed angiotensin II-induced neonatal rat cardiomyocyte hypertrophy in vitro. Mechanistically, Sesn2 overexpression increased AMPKα2 phosphorylation but inhibited mTORC1 phosphorylation. The cardiac protections of Sesn2 overexpression were also via regulating oxidative stress by enhancing Nrf2/HO-1 signaling, restoring SOD activity, and suppressing NADPH activity. Particularly, we first proved the vital role of AMPKα2 in the regulation of Sesn2 with AMPKα2 knockout (AMPKα2-/-) mice and Sesn2 transgenic mice crossed with AMPKα2-/-, since Sesn2 overexpression failed to improve cardiac function, inhibit cardiac hypertrophy and fibrosis, and attenuate oxidative stress after AMPKα2 knockout.

Conclusion: This study uniquely revealed that Sesn2 overexpression showed little genetic toxicity in mice hearts and inhibited mTORC1 activation and oxidative stress to protect against pressure overload-induced cardiac hypertrophy in an AMPKα2 dependent pathway. Thus, interventions through promoting Sesn2 expression might be a potential strategy for treating pathological cardiac hypertrophy and heart failure.

REDD1 attenuates hepatic stellate cell activation and liver fibrosis via inhibiting of TGF-β/Smad signaling pathway

Liver fibrosis is caused by repetitive hepatic injury. Regulated in development and DNA damage response 1 (REDD1) gene is induced by various stresses and has been studied in cell proliferation and survival. However, the role of REDD1 in hepatic stellate cell activation and hepatic fibrogenesis has not yet been investigated. In the current study, we examined the effect of REDD1 on hepatic fibrogenesis and the underlying molecular mechanism. REDD1 protein was upregulated in the activated primary hepatic stellate cells and transforming growth factor-β (TGF-β)-treated LX-2 cells. REDD1 mRNA levels were also elevated by TGF-β treatment. TGF-β signaling is primarily transduced via the activation of the Smad transcription factor. However, TGF-β-mediated REDD1 induction was not Smad-dependent. Thus, we investigated the transcription factors that influence the REDD1 expression by TGF-β. We found that c-JUN, a component of AP-1, upregulated the REDD1 expression that was specifically suppressed by p38 inhibitor. In silico analysis of the REDD1 promoter region showed putative AP-1-binding sites; additionally, its deletion mutants demonstrated that the AP-1-binding site between -716 and -587 bp within the REDD1 promoter is critical for TGF-β-mediated REDD1 induction. Moreover, REDD1 overexpression markedly inhibited TGF-β-induced plasminogen activator inhibitor-1 (PAI-1) expression and Smad phosphorylation. REDD1 adenovirus infection inhibited CCl₄-induced hepatic injury in mice, which was demonstrated by reduced ALT/AST levels and collagen accumulation. In addition, we observed that REDD1 inhibited CCl₄-induced fibrogenic gene induction and restored GSH and malondialdehyde levels. Our findings implied that REDD1 has the potential to inhibit HSC activation and protect against liver fibrosis.

The potential role of sestrin 2 in liver regeneration

Liver regeneration is a remarkably complex phenomenon conserved across all vertebrates, enabling the restoration of lost liver mass in a matter of days. Unfortunately, extensive damage to the liver may compromise this process, often leading to the death of affected individuals. Ischemia/reperfusion injury (IRI) is a common source of damage preceding regeneration, often present during liver transplantation, resection, trauma, or hemorrhagic shock. Increased oxidative stress and mitochondrial dysfunction are key hallmarks of IRI, which can jeopardize the liver's ability to regenerate. Therefore, a better understanding of both liver regeneration and IRI is of important clinical significance. In the current review, we discuss the potential role of sestrin 2 (SESN2), a novel anti-aging protein, in liver regeneration and ischemia/reperfusion preceding regeneration. We highlight its beneficial role in protecting cells from mitochondrial dysfunction and oxidative stress as key aspects of its involvement in liver regeneration. Additionally, we describe how its ability to promote the expression of Nrf2 bears significant importance in this context. Finally, we focus on a potential novel link between SESN2, mitohormesis and ischemic preconditioning, which could explain some of the protective effects of preconditioning.

Regulatory mechanisms of Sesn2 and its role in multi-organ diseases

Sestrin2 (Sesn2) is a powerful anti-oxidant that can prevent acute and chronic diseases. The role of Sesn2 has been thoroughly reviewed in liver, nervous system, and immune system diseases. However, there is a limited number of reviews that have summarized the effects of Sesn2 in heart and vascular diseases, and very less literature-based information is available on involvement of Sesn2 in renal and respiratory pathologies. This review summarizes the latest research on Sesn2 in multi-organ stress responses, with a particular focus on the protective role of Sesn2 in cardiovascular, respiratory, and renal diseases, emphasizing the potential therapeutic benefit of targeting Sesn2 in stress-related diseases.

The emerging role of ferroptosis in non-cancer liver diseases: hype or increasing hope?

Ferroptosis is an iron- and lipotoxicity-dependent form of regulated cell death (RCD). It is morphologically and biochemically distinct from characteristics of other cell death. This modality has been intensively investigated in recent years due to its involvement in a wide array of pathologies, including cancer, neurodegenerative diseases, and acute kidney injury. Dysregulation of ferroptosis has also been linked to various liver diseases and its modification may provide a hopeful and attractive therapeutic concept. Indeed, targeting ferroptosis may prevent the pathophysiological progression of several liver diseases, such as hemochromatosis, nonalcoholic steatohepatitis, and ethanol-induced liver injury. On the contrary, enhancing ferroptosis may promote sorafenib-induced ferroptosis and pave the way for combination therapy in hepatocellular carcinoma. Glutathione peroxidase 4 (GPx4) and system x_c⁻ have been identified as key players to mediate ferroptosis pathway. More recently diverse signaling pathways have also been observed. The connection between ferroptosis and other forms of RCD is intricate and compelling, where discoveries in this field advance our understanding of cell survival and fate. In this review, we summarize the central molecular machinery of ferroptosis, describe the role of ferroptosis in non-cancer hepatic disease conditions and discuss the potential to manipulate ferroptosis as a therapeutic strategy.

A new insight into the intestine of Pacific white shrimp: Regulation of intestinal homeostasis and regeneration in Litopenaeus vannamei during temperature fluctuation

Litopenaeus vannamei (L. vannamei) is an essential aquaculture shrimp throughout the world, but its aquaculture industry is threatened by temperature fluctuation. In this study, our histological results indicated that the shrimp intestine has a self-repairing ability during temperature fluctuation; however the potential mechanisms were still unknown. Therefore, transcriptome profiles of the intestine were collected from shrimp at 28 °C (C28), 13 °C (T13) and 28 °C after their temperature rose back (R28) and were analyzed. A total of 2229 differentially expressed genes (DEGs) (986 up- and 1243 downregulated) were identified in the C28 group, and 1790 DEGs (933 up- and 857 downregulated) were identified in the R28 group when compared to their expression levels in the T13 group. According to the functional annotation using KEGG, we found that the immune system was the most enriched section of organismal systems and that the shrimp can mobilize the body's immune response to regulate organism homeostasis during temperature fluctuation, although cold stress decreased the immunity. Additionally, metabolic inhibition is a strategy to cope with cold stress, and the regulation of lipid metabolism was especially important for shrimp during temperature fluctuation. Remarkably, the Hippo signaling pathway might help the repair of intestinal structure. Our research provides the first histological analysis and transcriptome profiling for the L. vannamei intestine during the temperature fluctuation stage. These results enrich our understanding of the mechanism of intestinal self-repair and homeostasis and could provide guidance for shrimp farming.

Sestrin 2 attenuates sepsis-associated encephalopathy through the promotion of autophagy in hippocampal neurons

Sepsis‐associated encephalopathy (SAE) has typically been associated with a poor prognosis. Although sestrin 2 (SESN2) plays a crucial role in metabolic regulation and the stress response, its expression and functional roles in SAE are still unclear. In the present study, SAE was established in mice through caecal ligation and puncture (CLP). The adeno‐associated virus 2 (AAV2)‐mediated SESN2 expression (ie overexpression and knockdown) system was injected into the hippocampi of mice with SAE, and subsequently followed by electron microscopic analysis, the Morris water maze task and pathological examination. Our results demonstrated an increase of SESN2 in the hippocampal neurons of mice with SAE, 2‐16 hours following CLP. AAV2‐mediated ectopic expression of SESN2 attenuated brain damage and loss of learning and memory functions in mice with SAE, and these effects were associated with lower pro‐inflammatory cytokines in the hippocampus. Mechanistically, SESN2 promoted unc‐51‐like kinase 1 (ULK1)‐dependent autophagy in hippocampal neurons through the activation of the AMPK/mTOR signalling pathway. Finally, AMPK inhibition by SBI‐0206965 blocked SESN2‐mediated attenuation of SAE in mice. In conclusion, our findings demonstrated that SESN2 might be a novel pharmacological intervention strategy for SAE treatment through promotion of ULK1‐dependent autophagy in hippocampal neurons.

Sestrin2: Its Potential Role and Regulatory Mechanism in Host Immune Response in Diseases

Sestrin2 (SESN2), a highly evolutionarily conserved protein, is critically involved in cellular responses to various stresses. SESN2 has a protective effect on physiological and pathological states mainly via regulating oxidative stress, endoplasmic reticulum stress, autophagy, metabolism, and inflammation. In recent years, breakthrough investigations with regard to the regulation and signaling mechanisms of SESN2 have markedly deepened our understanding of its potential role as well as its significance in host response. However, the functions of SESN2 in the immune system and inflammation remain elusive. It has been documented that many immune cells positively express SESN2 and, in turn, that SESN2 might modulate cellular activities. This review incorporates recent progress and aims to provide novel insight into the protective role and regulatory pathway of SESN2, which acts as a potential biomarker and therapeutic target in the context of various diseases.

cis Elements that Mediate RNA Polymerase II Pausing Regulate Human Gene Expression

Aberrant gene expression underlies many human diseases. RNA polymerase II (Pol II) pausing is a key regulatory step in transcription. Here, we mapped the locations of RNA Pol II in normal human cells and found that RNA Pol II pauses in a consistent manner across individuals and cell types. At more than 1,000 genes including MYO1E and SESN2, RNA Pol II pauses at precise nucleotide locations. Characterization of these sites shows that RNA Pol II pauses at GC-rich regions that are marked by a sequence motif. Sixty-five percent of the pause sites are cytosines. By differential allelic gene expression analysis, we showed in our samples and a population dataset from the Genotype-Tissue Expression (GTEx) consortium that genes with more paused polymerase have lower expression levels. Furthermore, mutagenesis of the pause sites led to a significant increase in promoter activities. Thus, our data uncover that RNA Pol II pauses precisely at sites with distinct sequence features that in turn regulate gene expression.

Inhibitory Effect of Sestrin 2 on Hepatic Stellate Cell Activation and Liver Fibrosis

Aims: Hepatic fibrosis results from chronic liver injury and inflammatory responses. Sestrin 2 (Sesn2), an evolutionarily conserved antioxidant enzyme, reduces the severities of acute hepatitis and metabolic liver diseases. However, the role of Sesn2 in the pathogenesis of liver fibrosis remains obscure. Here, we used cultured hepatic stellate cells (HSCs) and chronic carbon tetrachloride (CCl₄) and bile duct ligation (BDL) murine models to investigate the effects of Sesn2 on fibrogenesis. Results: Sesn2 protein and mRNA levels were upregulated in activated primary HSCs, and by increasing transcription, transforming growth factor-β (TGF-β) also increased Sesn2 expression in HSCs. Furthermore, Smad activation was primarily initiated by TGF-β signaling, and Smad3 activation increased Sesn2 luciferase activity. In silico analysis of the 5' upstream region of the Sesn2 gene revealed a putative Smad-binding element (SBE), and its deletion demonstrated that the SBE between -964 and -956 bp within human Sesn2 promoter was critically required for TGF-β-mediated response. Moreover, ectopic expression of Sesn2 reduced gene expressions associated with HSC activation, and this was accompanied by marked decreases in SBE luciferase activity and Smad phosphorylation. Infection of recombinant adenovirus Sesn2 reduced hepatic injury severity, as evidenced by reductions in CCl₄- or BDL-induced alanine aminotransferase and aspartate aminotransferase, and inhibited collagen accumulation. Furthermore, HSC-specific lentiviral delivery of Sesn2 prevented CCl₄-induced liver fibrosis. Finally, Sesn2 expression was downregulated in the livers of patients with liver cirrhosis and in mouse models of hepatic fibrosis. Innovation and Conclusion: Our findings suggest that Sesn2 has the potential to inhibit HSC activation and hepatic fibrosis.

Protective effect of sestrin2 against iron overload and ferroptosis-induced liver injury

Ferroptosis is the non-apoptotic form of cell death caused by small molecules or conditions that inhibit glutathione biosynthesis or resulting in iron-dependent accumulation of lipid peroxidation by lipid reactive oxygen species (ROS). Sestrin2 (Sesn2), a conserved antioxidant protein, is responsive to various stresses including genotoxic, metabolic, and oxidative stresses and acts to restore homeostatic balance. Sesn2 expression was reported to be regulated via stress-responsive transcription factors including p53, Nrf2, and HIF-1α. However, the role of Sesn2 in regulating ferroptosis is not known. In the current study, we investigated whether ferroptosis inducing compounds including erastin, sorafenib, and buthionine sulfoximine affect Sesn2 expression and the role of Sesn2 in cytoprotection against ferroptosis-mediated cell death. Our data demonstrate that ferroptosis inducers significantly increased Sesn2 in hepatocytes in a dose- and time-dependent manner. Treatment with erastin upregulated Sesn2 mRNA levels and luciferase reporter gene activity, and erastin-mediated Sesn2 induction was transcriptionally regulated by NF-E2-related factor 2 (Nrf2). Furthermore, deletion of the antioxidant response element (ARE) in the Sesn2 promoter or Nrf2 knockout or knockdown abolished erastin-induced Sesn2 expression. In cells expressing Sesn2, erastin-induced cell death, ROS formation, and glutathione depletion were almost completely inhibited compared to that in control cells. Treatment with phenylhydrazine in mice, well-reported iron overload liver injury model, increased ALT and AST levels and altered histological features, which were almost completely inhibited by adenoviral Sesn2 infection. Collectively, our results suggest that ferroptosis-mediated Sesn2 induction is dependent on Nrf2 and plays a protective role against iron overload and ferroptosis-induced liver injury.

Sestrin 2 protects against metabolic stress in a p53-independent manner

Glucose limitation activates p53, which functions as an adaptive response to maintain cell survival. However, p53 is frequently deleted or mutated in a variety of tumors, while most cancer cells can acclimatize themselves to metabolically unfavorable surrounding, indicating that alternative mechanisms other than p53 transactivation underly adaptive response of cancer cells with p53 deletion or mutation to metabolically hostile environment. Sestrin 2 (SESN2) is a p53 downstream target, which plays a protective role against various stressful stimuli, such as genotoxic, energetic, and oxidative stress. In the current study, we demonstrated that SESN2 transcript was stabilized by glucose limitation at the posttranscriptional level irrespective of p53 status. Importantly, SESN2 also protected cells from metabolic stress triggered by glucose limitation in a p53-independent manner. Our data indicated that stabilization of SESN2 transcript might be an alternative adaptive response to metabolic stress other than p53 activation. Thereby, the current study highlights the significance of stabilization of SESN2 transcript in adaptation of cells with p53 deletion or mutation to metabolic stress.

Arsenic trioxide-mediated suppression of miR-182-5p is associated with potent anti-oxidant effects through up-regulation of SESN2

Arsenic trioxide (ATO) is a traditional Chinese medicine that can induce oxidative stress for treatment of cancer cells. However, ATO may generate anti-oxidative responses to compromise the cytotoxic effect, but the underlying mechanisms remain unclear. Here we found that ATO could inhibit miR-182-5p expression in patient-derived primary S1 glioblastoma (GBM) cells accompanied by up-regulation of Sestrin-2 (SESN2) mRNA, a known anti-oxidant molecule. This phenomenon was also detected in a U87MG glioma cell line, human lung adenocarcinoma H1299 cell line and A549 cell line. Pretreatment with a free radical scavenger N-acetylcysteine (NAC) reduced the oxidative stress induced by ATO. Concomitantly, ATO mediated suppression of miR-182-5p and enhancement of SESN2 expression were also compromised. The MTT assay further showed that ATO induced cytotoxicity was enhanced by transfection of miR-182-5p mimics. Overexpression of miR-182-5p mimics significantly suppressed the expression of SENS2 and a firefly luciferase reporter gene fused to 3’- untranslated region (UTR) of SESN2 mRNA. Use of ribonucleoprotein immunoprecipitation (RNP-IP), ATO mediated suppression of miR-182-5p led to the stabilization of SESN2 mRNA as a result of Argonaute-2 (AGO2) dependent gene silencing. Furthermore, high expression of miR-182-5p and low expression of SESN2 mRNA tend to be associated with longer survival of glioma or lung cancer patients using public available gene expression datasets and online tools for prediction of clinical outcomes. Taken together, current data suggest that the miR-182-5p/SENS2 pathway is involved in ATO induced anti-oxidant responses, which may be important for the design of novel strategy for cancer treatment.

Evaluation of Plasma TRB3 and Sestrin 2 Levels in Obese and Normal-Weight Children

OBJECTIVE

Obesity in childhood and adolescence is associated with metabolic syndrome and cardiovascular diseases. TRB3 (Tribbles homolog 3) and sestrin 2 are two newly found proteins that have been identified to play an important role in obesity and its complications.

AIM

The purpose of this study was to evaluate concentrations of TRB3 and sestrin 2 in plasma of obese and normal-weight children and adolescents, and their association with metabolic and anthropometric parameters.

METHODS

Plasma levels of TRB3, sestrin 2, insulin, fasting plasma glucose (FPG), and lipid profile were evaluated in 70 children and adolescents (34 obese and 36 controls). Insulin resistance was calculated using a homeostasis model assessment of insulin resistance. Metabolic syndrome was defined according to IDF criteria.

RESULTS

Plasma TRB3 levels of the obese subjects were significantly higher than that of normal weight subjects. TRB3 levels were positively correlated with BMI, BMI z-score, waist circumference, and FPG. The concentration of sestrin 2 was significantly lower in obese subjects compared to normal-weight subjects. A statistically significant positive correlation was observed between plasma concentrations of sestrin 2 and high-density lipoprotein cholesterol. Neither TRB3 nor sestrin 2 were correlated with insulin resistance and metabolic syndrome.

CONCLUSION

Both TRB3 and sestrin 2 may contribute to the development of obesity and its complications and can be considered interesting therapeutic target for the treatment of obesity.